Molecular chaperones are protein machines that are responsible for the correct folding, stabilization, and function of other proteins in the cell. Exposure of cells to environmental stress, including heat shock, alcohols, heavy metals or oxidative stress, results in the cellular accumulation of these chaperones, commonly known as heat shock proteins (Hsp's). Heat-shock protein 90 (Hsp90) constitutes about 1-2% of total cellular proteins and is usually present in the cell as a dimer. It is a molecular chaperone responsible for ATP-depended folding, stability and function of many “client” proteins that are involved in the development and progression of cancer. These client proteins include ErbB2, c-Raf, Cdk4, mutant p53, hTERT, Hifl-α, and the estrogen/androgen receptors. Inhibition of Hsp90 causes the simultaneous, combinatorial destabilization and degradation of the oncogenic client proteins, leading in turn to a multiprolonged attack on all of the hallmark traits of cancer, including unrestricted proliferation and survival, invasion, metastasis and angiogenesis. It is generally thought that cancer cells are more susceptible to Hsp90 inhibition than are the corresponding normal cells (P. Workman (2004), Trends Mol. Med., 10, 47-51). On the other hand, therapeutic selectivity of Hsp90 inhibitors is the stressed condition of cancer cells, due both to oncogenic mutations and deregulated signalling and also to environmental factors such as hypoxia, acidosis and nutrient deprivation. Moreover, it has been reported that the Hsp90 found in malignant cells exists predominantly in a superchaperone complex that binds Hsp90 inhibitors much more effectively than the uncomplexed form that is mainly present in healthy cells (B. W. Dymock et al, (2004), Expert Opin. Ther. Patents, 14, 837-847).
The ATPase activity of Hsp90 chaperone can be inhibited with some selectivity by natural product antibiotics such as geldanamycin and radicicol (S. M. Roe et al, (1999), J Med Chem 42, 260-266). Both of those compounds bind to the N-terminal domain of Hsp90 and inhibit the intrinsic ATPase activity.
Geldanamycin showed activity in human tumour xenograft models but this compound proved to be too hepatotoxic for clinical development. However, the modified versions of geldanamycin—17-allylamino-17-demethoxy-geldanamycin (17-AAG) and 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) retain the property of Hsp90 inhibition and have significantly less hepatotoxicity than geldanamycin (U.S. Pat. No. 4,261,989, publ. 1981). 17-AAG is currently being evaluated in clinical trials.
Radicicol is macrocyclic antibiotic isolated from Monosporium Bonorden. Radicicol is more potent inhibitor of Hsp90 ATPase activity than geldanamycin or 17-AAG (T. W. Schulte et al, (1998) Cell Stress Chaperones 3, 100-108). Unfortunately, the radicicol structure has some inherent limitations, including the epoxide moiety, keto group ant the propensity to undergo Michael addition reactions. Radicicol lacks antitumour activity in vivo due to the unstable chemical nature of the compound. Oxime derivatives of radicicol (known as KF25706 and KF58333) have been synthesized and retain the Hsp90 inhibitory activity of radicicol. Moreover KF25706 has been shown to exhibit in vivo antitumour activity in human tumour xenograft models (S. Soga et al (1999) Cancer Res, 59, 2931-8; U.S. Pat. No. 6,239,168; U.S. Pat. No. 6,316,491; U.S. Pat. No. 6,635,662). However, no radicicol derivative has progressed to clinical development.
It is also known that coumarin, novobiocin, and cisplatin bind to the C-terminal domain of Hsp90 resulting in the inhibition of ATPase function (G. A. Holdgate (1997) Biochemistry 36, 9663-9673; R. J. Lewis (1996) Embo J 15, 1412-1420; M. G. Marcu et al (2000) J. Biol. Chem., 275, 37181-37186; M. G. Marcu et al (2003) Curr. Cancer Drug Targets, 3, 343). Therefore, both binding sites of Hsp90 are important to Hsp90 chaperone properties.
Significant consideration in the patent literature is given to various synthetic small molecule Hsp90 inhibitors. First purine-based inhibitors (PU3 and PU24FCl) have been synthesized based on rational drug design with the aid of the X-ray crystal structure (EP 1335920, G. Chiosis et al (2001) Chem. Biol. 8, 289-299). These agents were shown to result in the degradation of signaling molecules, including ERBB2, and to cause cell cycle arrest and differentiation in breast cancer cells. Recently, S. R. Kasibhatla et al have reported about novel purine derivatives with amine, sulfide, sulfoxide and sulfone moieties (WO 03037860; U.S. Pat. No. 7,241,890; U.S. Pat. No. 7,138,401). Some of these compounds inhibit Hsp90 chaperone in nanomolar potency. Nowadays purine-based inhibitors of Hsp90 attract scientific attention (WO2006075095, EP1838322).
Another class of synthetic Hsp90 inhibitors are presented by structural purine analogs—pyrazolopyrimidines, pyrrolopyrimidines and triazolopyrimidines. These compounds were synthesized and tested by S. R. Kasibhatla et al (U.S. Pat. No. 7,148,228; U.S. Pat. No. 7,138,402, U.S. Pat. No. 7,129,244, EP1869027).
Various 3,4-diarylpyrazole derivatives bearing resorcinol moiety have been selected and prepared by high throughput screening of a combinatorial library at the Institute of Cancer Research. Some of such derivatives (known as CCT 018159, VER 49009) showed very high Hsp90 inhibition affinity (K. M. J. Cheung et al (2005) Bioorg. Med. Chem. Lett., 15, 3338-3343; B. W. Dymock et al (2005) J. Med. Chem., 48, 4212-4215; U.S. Pat. No. 7,247,734; EP 1456180). A number of 3-arylpyrazole-4-piperazine derivatives (X. Barril (2006) Bioorg. Med. Chem. Lett., 16, 2543-2548), as well as 3-aryl-4-aryloxypyrazoles (patent JP 2005225787) are synthesized and exhibited Hsp90 binding affinity.
It is also patented that pyrazole scaffold in 3,4-diarylpyrazoles can be replaced by other 5-membered ring, such as isoxazole (EP1611112) or triazole (WO2005000300, WO2007139952).
Also a large number of small-molecule synthetic inhibitors of Hsp90 chaperone have been synthesized and evaluated. This is different pyrazole (US2007112192, EP1567151, US2007191445, EP1620090, JP2006306755), triazole (US2007155809, WO2007139956, WO2008021364, WO2006055760, WO2007139968, WO2007139967, WO2007139952, US2006167070), quinazolines (EP1885701, WO2006122631), isoindoles (WO2008044034, EP 1869042) and hydroxybenzamides (WO2006109075).
Despite the fact that a large number of different Hsp90 inhibitors have been synthesized to date, only few of them are clinically tested. There still remains a great need of new potent Hsp90 inhibitors which offer one or more following advantages: improved activity, selectivity, solubility, reduced toxicity and side-effects, reduced cost of synthesis and so on.
Therefore, the creation of novel Hsp90 chaperone inhibitors is still an important task.
No data on synthesis of invention compounds 5-aryl-4-(5-substituted 2,4-dihydroxyphenyl)-1,2,3 thiadiazoles and intermediate compounds required for the synthesis of invention compounds was found in patent and non-patent literature.